Anionic polymerization of ɛ-caprolactam in the presence of piperidine N-carboxamides

Piperidine N-carboxamides were shown to activate the anionic polymerization of ?-caprolactam. The activator structure affects properties of the resulting polycaproamide.     

Syntheses of fluoroalkyl derivatives of two biologically active oligopeptides

Fluoroalkyl derivatives of two biologically active oligopeptides [ enkephalin,[(m-C2F4Cl)Tyr1]-Leu-enkephalin and [(m-COCF2Cl)Tyr2]-melanocyte-stimulating hormone releasing hormone have been synthesized.Studies on the activities of these peptides are underway.     

Anionic polymerization of ϵ-caprolactam—LX. Ionization and solvation changes in the initial stage of the anionic polymerization of lactams in tetrahydrofuran

Interactions between potassium salts of lactams and N-acyllactam propagation centres in the initial stage of the anionic polymerization of lactams were studied by measuring changes in the electric conductivity and in the i.r. spectrum in the range of carbonyl vibration bands of these compounds and of the corresponding derivatives of open-chain alkylamides in tetrahydrofuran. The gradual rise in conductivity and u.v. absorption around 300 nm observed with these systems can be attributed to the formation of 3-oxoimide and 3-oxoamide structures by the condensation of imides.     

Cationic polymerization of 1,3-pent adiene in the presence of arenes

The cationic polymerizations of 1,3-pentadiene initiated by AlCl3 in n-hexane at 30℃ have been carried out in the presence of various arenes,i.e.,benzene,toluene,p-xylene,o-xylene,m-xylene and mesitylene.The presence of all these arenes have reduced in different degrees the formation of crossliuked products.Namely,the crosslinking reaction,a major side-reaction during the cationic polymerization of 1,3-pentadiene,has been suppressed by adding the aromatic compounds.The results showed that a chain transfer to arene took place and this transfer process hindered the generation of the crosslinked polymer.IR and 1H NMR spectra have confirmed the existence of the corresponding aryl groups in the resulting polymers.     

Electrochemical polymerization of dicarboxylic acids—VI. Mechanism of polymerization

The mechanism of the electrochemical polymerization of dicarboxylic acids in various solvents, which also leads to the formation of various side products, is discussed. The formation of hydrocarbons was rationalized through the formation of α,ω-biradicals which suffer coupling or disproportionation reactions. Carboxylic acids are shown to originate from reactions of ^•(CH₂)_k COOH radicals which couple radicals which couple or disproportionate among themselves or other radicals to give saturated and unsaturated acids. Cations formed from anodic oxidation of the radicals are the precursors of lactones and some olefins. The conformations of the dicarboxylate anions at the anode surface are discussed with a view of rationalizing the formation of the various products. Polymer formation was explained as occurring through α,ω-biradicals having a definite conformation. Pyridine affected to a large extent these conformations, and higher concentrations of pyridine led to an increase in the conformations which lead to polymer formation.     

β-Peptide coatings by surface-initiated polymerization

Homopolymers of β-lactams can be grown by surface-initiated polymerization. These surface-linked β-peptides are living polymers with the potential to be utilized as tunable, protease-resistant interfaces in multiphase structural composites where the characteristics of the interface influence bulk properties.     

Ring-opening polymerization of l-lactide in the presence of α-hydroxy-γ-butyrolactone

Among the polymer families, aliphatic polyesters stand out from this category thanks to their degradable and biocompatible properties. In particular, the γ-lactones differ from other lactones by yielding polyesters that can be depolymerized back to the monomer and offer the advantage of counting various biobased monomers. As an example, α-hydroxy-γ-butyrolactone (HBL) is a hydroxy-functionalized monomer that can be obtained by a biological synthetic route from glucose. In this article, the ring-opening copolymerization (ROCP) of HBL and l -lactide (LLA) using t-BuP₄ as catalyst is investigated. The copolymerizations were conducted within a temperature range of 5–100°C, affording monomer conversions exceeding 80%. The characterization of the copolyesters revealed a branched structure consisting of different HBL patterns, including cyclic, linear, and branched motives. Performing a kinetic study of the copolymerization at room temperature provided a deeper understanding of the mechanism. By modulating the reaction parameters, copolymers of low molar masses with an HBL content of up to 33% were synthesized. High molar mass LLA/HBL-based copolyesters, with $$ up to 290,000 g/mol, were synthesized by a straightforward chain coupling reaction with a diisocyanate.     

Phase state of iron system colloidal catalyst in butadiene polymerization

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Model of “living” active centers in kinetics of the solid-phase polymerization

A model of “living” active centers in the solid phase has been developed, which are the complexes of a traditional active center (radical or ion) with a carrier of excessive free volume in solids, the structural defect (vacancy, polyvacancy, dislocation, crack). This model for the first time successfully explained the most nontrivial kinetic peculiarities of the solid-phase polymerization.     

Crosslinking reaction in the cationic polymerization of 1, 3-pentadiene

The cationic polymerization of 1,3-pentadiene (PD) initiated by AlCl_3 in n-hexane was carried out. Effects of arenes, alkyl halides and ethers on the gel formation resulting from crosslinking reaction were investigated. The erosslinking was reduced by various arenes through a chain transfer mechanism. Alkyl halides such as tert-butyl chloride and allyl chloride could complex with AlCl_3 to generate an initiating system giving rise to a gel-free polymerization, while benzyl chloride reduced the formation of gel by chain transfer. Ethers exerted two effects on the polymerization system: giving a complex initiating system with AlCl_3 to produce a relatively high molecular weight polymer, or reducing crosslinking by lowering activity of carbocations.     

Flame retardant polyamide 6 by in situ polymerization of ε-caprolactam in the presence of melamine derivatives

An improved method for preparing melamine cyanurate （MCA） based flame retardant polyamide 6 （FRPA6） materials has been proposed. This processing method, i.e., improved in situ polymerization, was used to synthesize flame retardant PA6. In situ formed MCA nanoparticles were supposed to be linked to PA6 chains in the ε-caprolactam hydrolytic polymerization system to obtain startype polymers for the first time. Through TEM photographs, it can be found that the in situ formed MCA nanoparticles with diametric size of less than 50 nm, are nanoscaled, highly uniformly dispersed in the PA6 matrix. Synthesized flame retardant PA6 have good fire performance which can achieve UL-94 V-0 rating at 1.6 mm thickness with the presence of 7.34 wt.% MCA in the matrix.     

6-Membered ring intermediates in polymerization of N-carboxyanhydride-L-α-arginine in H_2O

In polymerization of N-carboxyanhydride-L-α-arginine(L-Arg-NCA) in H2O,nucleophilic reaction of guanidine group with the carbonyl group of L-Arg-NCA leads to quick intramolecular rearrangement,yielding a 6-membered ring intermediate 1-amidino-3-amino-2-piperidone,which is either elongated by another L-Arg-NCA yielding arginyl-1-amidino-3-amino-2-piperidone or hydrolyzed to L-α-arginine.The oligoarginines are formed mainly through hydrolysis of arginyl-1-amidino-3-amino-2-piperidones.This is a unique pathway...     

Flame retardant polyamide 6 by in situ polymerization of ε-caprolactam in the presence of melamine derivatives

An improved method for preparing melamine cyanurate (MCA)based flame retardant polyamide 6 (FRPA6)materials has been proposed.This processing method,i.e.,improved in situ polymerization,was used to synthesize flame retardant PA6.In situ formed MCA nanoparticles were supposed to be linked to PA6 chains in the ε-caprolactam hydrolytic polymerization system to obtain startype polymers for the first time.Through TEM photographs,it can be found that the in situ formed MCA nanoparticles with diametric size of less than 50 nm,are nanoscaled,highly uniformly dispersed in the PA6 matrix.Synthesized flame retardant PA6 have good fire performance which can achieve UL-94 V-0 rating at 1.6 mm thickness with the presence of 7.34 wt.% MCA in the matrix.     

Kinetic features of short-time polymerization of isoprene in the presence of supported titanium–magnesium catalyst

Short-time polymerization of isoprene under the action of supported titanium–magnesium catalyst is carried out. The pulsation mixing of the reagent flows and the unit design features allow one to reduce the average residence time of reagents in the reaction zone and to study the first 0.7 s of the isoprene polymerization. It is found that, very early in polymerization, the propagation of polyisoprene macromolecules proceeds on the surface of the primary aggregates of catalyst particles characteristic of a high trans-1,4 specificity via the “living” mechanism with a high rate. Furthermore, the fragmentation of the initial aggregates of the catalyst particles occurs, which results in formation of new polymerization centers, a decrease in the average molecular masses of polyisoprene, and a broadening of the polymer MMD. The results are explained by the existence of a range of the kinetic continuity of the rapid initiation stage and several subsequent stages of macromolecule propagation, followed by a significant decrease in the chain propagation rate constant compared to the initiation constant.     

Acidic ionic liquids catalyst in homo and graft polymerization of ε-caprolactone

Biodegradable polycaprolactone was prepared by ring-opening polymerization in presence of ionic liquids as efficient, inexpensive, nontoxic, and easily handled acid catalysts. The resulting polymer exhibited good yield and inherent viscosity between 0.10 and 0.18 dL/g. The chemical structure of obtained polymer was verified by the ¹H-NMR and Fourier transform infrared spectroscopy (FT-IR) spectra. In continuation, the obtained polymer was applied to improve quality level and mechanical properties and also to reduce the hydrophilic properties of the starch, so the ring-opening polymerization of ε-caprolactone was investigated in the presence of starch hydroxyl groups as initiator and ionic liquid as catalyst. The obtained starch-grafted-polycaprolactone was verified by ¹H-NMR, FT-IR spectra, and field emission scanning electron microscopy analysis.     

Dynamic rheology studies of in situ polymerization process of polyacrylamide–cellulose nanocrystal composite hydrogels

A series of dynamic small-amplitude oscillatory shear experiments for in situ polymerization process of polyacrylamide–cellulose nanocrystal (PAM–CNC) nanocomposite hydrogels were performed to investigate the relationship between rheological properties and synthesis parameters including chemical cross-linker concentration, polymerization temperature, initiator concentration, and CNC aspect ratios. The results showed that CNCs accelerated the onset of gelation (t _onset) and acted as a multifunctional cross-linker during the gelation reaction. The composite hydrogels exhibited enhanced steady-state elastic modulus ( G_￥￠ ) \left( {G_\infty^\prime } \right) and plateau loss factor (tanδ) compared to these of the pure PAM hydrogels, indicating that adding CNCs not only reinforced but also toughened PAM hydrogels. ( G_￥￠ ) \left( {G_\infty^\prime } \right) and the effective network junction density (N) increased with increased cross-linker concentration, polymerization temperature, and CNC aspect ratios, but decreased with increased initiator concentration. The changes of plateau tanδ were opposite to that of G_￥￠ G_\infty^\prime . The sol–gel transition kinetics of PAM–CNC hydrogels accelerated with increased cross-linker concentration and polymerization temperature and, however, reached optimization at 0.25 wt% of initiator concentration. CNCs with lower aspect ratios promoted t _onset and the sol–gel transition of PAM–CNC hydrogels, suggesting the fact that CNCs with lower aspect ratios further facilitated the formation of network of PAM–CNC nanocomposite hydrogels.     

Kinetics of radical polymerization—XLV. Steric effects in the radical reactivity of quinones

An attempt has been made to establish the dependence on structural parameters of the reactivity of substituted 1,4-benzoquinones as inhibitors in the radical polymerization of styrene. The relative reactivity depends on the redox potential of the quinone and on the size of the ortho-substituents. The steric factor has been separated from the overall reactivity and correlated with the extent of shielding of the reaction centre in the case of substituents of spherical symmetry.     

Tree-gel and loop-gel conversions in nonlinear polymerization

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